`sm_incr_ssc` performed an out of bounds write when `ssc` is bigger than
255. The local variable `ii` needs to be decremented instead of
incremented in the `for`-loop.
This was introduced in d30cd83a, wheras The previous implementation did
actually decrement `ii`, see d30cd83ad4
Fixes https://github.com/OpenSC/OpenSC/issues/785
